The present invention relates generally to fastener-driving tools, and more specifically to such tools operating under combustion power, also referred to as combustion nailers.
Combustion nailers are known in the art, and one type of such tools, also known as IMPULSE® brand tools for use in driving fasteners into workpieces, is described in commonly assigned patents to Nikolich U.S. Pat. Re. No. 32,452, and U.S. Pat. Nos. 4,522,162; 4,483,473; 4,483,474; 4,403,722; 5,197,646; 5,263,439 and 6,145,724, all of which are incorporated by reference herein. Similar combustion-powered nail and staple driving tools are available commercially from ITW-Paslode of Vernon Hills, Ill. under the IMPULSE®, BUILDEX® and PASLODE® brands.
Such tools incorporate a tool housing enclosing a power source in the form of a small internal combustion engine. The engine is powered by a canister of pressurized fuel gas, also called a fuel cell. A battery-powered electronic power distribution unit produces a spark for ignition, and a fan located in a combustion chamber provides for both an efficient combustion within the chamber, while facilitating processes ancillary to the combustion operation of the device. The engine includes a reciprocating piston with an elongated, rigid driver blade disposed within a single cylinder body.
Upon the pulling of a trigger switch, which causes the spark to ignite a charge of gas in the combustion chamber of the engine, the combined piston and driver blade is forced downward to impact a positioned fastener and drive it into the workpiece. The piston then returns to its original or pre-firing position through differential gas pressures within the cylinder. Fasteners are fed magazine-style into the nosepiece, where they are held in a properly positioned orientation for receiving the impact of the driver blade.
A valve sleeve is axially reciprocable about the cylinder and, through a linkage, moves to close the combustion chamber when a work contact element (WCE) at the end of the linkage is pressed against a workpiece. This pressing action also triggers a fuel-metering valve to introduce a specified volume of fuel into the closed combustion chamber.
Combustion-powered tools now offered on the market are sequentially operated tools. The tool must be pressed against the workpiece, collapsing the WCE before the trigger is pulled for the tool to fire a nail. The distinguishing feature that limits combustion-powered tools to sequential operation is the operator's manual control of the valve sleeve via a lockout mechanism that is linked to the trigger. This mechanism holds the combustion chamber closed until the operator releases the trigger, thus taking into account the operator's relatively slow musculature response time. In other words, the physical release of the trigger consumes enough time of the firing cycle to assure piston return. It is disadvantageous to maintain the chamber closed longer than the minimum time to return the piston, as cooling and purging of the tool is prevented.
In conventional combustion nailers, two electrical switches are required to obtain combustion-causing ignition. A first switch is referred to as a chamber switch or a head switch, and is closed when the reciprocating valve sleeve moves to seal the combustion chamber, through action of the WCE. To close the chamber switch, the tool is pressed against a workpiece where the fastener is desired. The second switch is the trigger switch, manipulated by the operator, which actually initiates the spark that generates combustion.
Combustion nailers are desired to be operable in at least one of two firing conditions. A first firing condition is called sequential, in that the chamber switch must be closed before the trigger switch can be pulled. A second firing condition is called repetitive, in which the user holds the trigger closed for an extended period of time, and ignition is initiated each time the chamber switch is closed. Repetitive firing is useful when a rapid rate of fastener application is desired. In either condition, one or both of the switches control other tool functions, such as a fan motor and/or solenoids for injecting fuel or maintaining the combustion chamber closed until the piston/driver blade returns to the pre-firing position.